[pure-silver] Re: Tonal gradation/smoothness in 35mm negs c.f. larger formats
----- Original Message ----- From: "Peter Badcock" <peter.badcock@xxxxxxxxx> 
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Monday, January 14, 2008 1:20 AM
Subject: [pure-silver] Re: Tonal gradation/smoothness in 35mm negs c.f. larger formats 



Hi Richard,
thanks for your reply. It certainly sounds like the difference in tonal smoothness is more than just a minor thing as you say "there is a noticeable difference between 35mm negs and anything larger". In fact you mentioned it here <http://www.freelists.org/archives/pure-silver/09-2007/msg00098.html>a 
few months ago in pure-silver.
I had also naively assumed that there were few good reasons to use a low accutance developer. So for 35mm it appears that there is a trade-off between accutance(sharpness) and tonal smoothness. This was also a new 
revelation for me.
I then realised that a chromogenic film like XP2 (which has no grain, but rather "dye clouds") inherently provides smoother tonality. I did a quick 
search and discovered a
post<http://photo.net/bboard/q-and-a-fetch-msg?msg_id=003EHC>by Mark 
Parsons to back up my deduction.
"This film (XP2) has very smooth tonal gradations, handles highlights very well, but seems to have very little edge effects. (High resolution but low apparent accutance - "fine" but not "sharp".) All of this adds up to a film that is (in my opinion) wonderful for most portraits and other "soft" scenes, but not the best for most landscapes and architecture"
Here is one follow-on thought/question. If I then use a low accutance developer with a fine grain/high res film like 100T-Max or Delta 100 in order to get good smoothness, could I then improve sharpness by unsharp 
masking? (without losing tonal smoothness)

regards
Peter
Chromogenic film does have grain because the dye is formed in proportion to the silver so the dye image mimics the original silver image. Kodak distinguishes between grain, which is a measurable quantity, and graniness, which is a perceived characteristic. They published a short treatice on that which I think is still on the Kodak web site. Acutance is a measure of perceived sharpness and is a term invented by Kodak for it. They found that edge contrast affected the perception of sharpness so that development in a way that exagerated the contrast of edges in an image would result in higher perceived sharpness. Acutance is not the same as resolution and the edge effects which produce acutance can actually reduce resolution. One reason low grain developers might also be low acutance is that they tend to have large amounts of sulfite. The main function of sulfite in a developer is to oxidize preferentially to the developing agent. Since edge effects are mostly the result of local exhaustion effects high sulfite developers tend to supress them. Acutance is desirable mostly in small negatives to compensate for lenses with low edge contrast or poor resolution. When one has a sharp lens this compensation may not be necessary or even desirable. Since the scale of the edge effects on the film is fixed the acutance boost is inversely proportional to the format size. Acutance effects are very noticable on 35mm negatives but hardly at all for 4x5. 

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx 
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